The article has four sections.
- Background information regarding the switchover
- Two of the most common problems
- Solutions to those problems
- Additional information for viewers receiving from Rowridge in Dorset, Wiltshire and NE Hampshire.
Frequencies and powers used by the Rowridge transmitter for digital TV services changed over three stages during March and April 2012. The first two stages were part of the digital switchover process and the final stage was a classed as a "later technical event".
- On 7th March 2012: Switchover stage 1 - Digital BBC (standard definition) services moved to their final frequencies and powers when BBC Two analogue was switched off.
- On 21st March 2012, Switchover stage 2 - Digital versions of ITV/C4/C5 and several digital spin off channels moved to their final frequencies and powers when all remaining analogue services were closed just after midnight. HD services launched, available with certified Freeview HD receivers.
- On 18th April 2012, Later technical event* - The extra commercial digital channels moved to final frequencies and powers. This couldn't be done at the time of switchover, because the frequencies assigned to the commercial providers couldn't be used until London had started stage 2 of their own switchover.
A retune was required on all three dates.
* It is referred to as a later technical event rather than "digital switchover stage 3" because the actual switchover to digital-only television had completed on the 21st March when the last remaining analogue services had closed. Various parts of the UK will experience future frequency changes for their TV signals that are not related to the actual switchover to digital TV.
Following the completion of these three events, there have been two distinct problems emerging.
#1. Viewers on or close to the Isle of Wight, with previously good signal, have suffered blockiness or breaking up.
#2. Viewers in Dorset, Wiltshire and northern parts of Hampshire receiving from Rowridge have lost channels from the early hours of the 18th April, and have not been able to get a good reception since then.
Some viewers may have had OK reception for a while after the events, but may encounter further issues when high pressure finally arrives to the UK during the summer months.
...to problem #1 Viewers living near to the transmitter site, or with good line of sight from their properties in the direction of the Isle of Wight may be getting a signal overload - which causes break up and other symptoms associated with a poor signal. If you have a signal strength close to 100%, but are experiencing break ups or picture distortion, the signal needs to be reduced in most cases.
Before switchover, the dignal signal was transmitted at an effective radiated power (ERP) of 20kW from the Rowridge mast. After switchover, services are being transmitted at up to 200 kW ERP. A significant boost. Therefore anyone that has an amplifier/booster needs to remove it where possible. Where it is not possible, or where there is no booster, an attenuator may be required. Electrical retailers sell aerial attenuators. (Google "aerial attenuators" for prices and stockists).
Furthermore, a reliable signal without the need for amplification may be gained by rotating the axis of your aerial by 90 degrees to vertical polarisation. More on this in #2. This may be true if you are getting interference from France.
...to problem #2 Viewers living further away, in Dorset, Wiltshire and in North Hampshire receiving from Rowridge (Isle of Wight) may now be prone to interference following the changes on the 18th April. There are a number of reasons why there may be more picture break-ups or loss of service:
1. The broadcasts from Rowridge to areas further away from the Isle of Wight are not optimised for viewers with existing aerial set ups.
2. You may be suffering from co-channel interference from the Stockland Hill transmitter in East Devon or from the Crystal Palace transmitter serving London.
3. The signal remains susceptible to co-channel interference in the summer months from broadcasts from France during periods of high pressure weather patterns.
Knowing that the TV services along the South Coast are more prone to continental interference but also knowing that the number of available frequencies is limited (which is why Channel 5 wasn't widely available on analogue from 1997), the frequency planners determined that post-switchover, they would boost the signal considerably. To reduce the effects of interference though, the strongest signals for all services would be transmitted using a separate set of antenna at the Rowridge transmitter sending vertically polarised signals. This would also mean a reduction of interference to and from other UK transmitters. For the normal TV viewer, this means that to get the best signal - especially further away from the Isle of Wight, the TV aerial needs rotating on its axis by 90 degrees.
Normally, aerials rigged for Rowridge reception are horizontally polarised, with the elements running across flat, so that e.g. birds can comfortably sit on them!
|Horizontally polarised aerials|
Whereas since the changes at Rowridge, viewers can get pick up the strongest signals by turning the aerials axis so that...
|Aerial set up for veritical polarised signals|
...the elements go from top to bottom. A bird couldn't sit on that very comfortably!
Will it make a big difference?
50 kW of effective radiated power is being used to transmit each commercial multiplex of channels to viewers who have the old horizontally polarised aerial set up. The vertically polarised signals are powered with 200kW of effective radiated power.
Additional information for viewers receiving from Rowridge in Dorset, Wiltshire and NE Hampshire.
- Dorset and Wiltshire
In Dorset, reception of the Rowridge transmitter (upto roughly Weymouth) is possible, with the best reception available if the aerial's axis is changed for verticially polarised signals (see above).
Viewers in Dorset and Wiltshire may locally be able to receive a reliable signal from the Mendip transmitter, near Wells in Somerset, if reception from Rowridge remains unreliable. This would involve changing the direction of the aerial, although there have been reports of people receiving Mendip with the aerial pointing toward Rowridge - although optimum reception is always achieved by moving the aerial to point in the direction of the desired transmitter. Mendip transmitter carries BBC and ITV West regional programmes. It is a well known fact that parts of Dorset and Wiltshire fall into a bit of black hole when it comes to regional programming, with locations a short distance apart being covered by different regional news programmes.
There is a transmitter in Salisbury transmitting all Freeview services that is an option in the Salisbury area, and there are a number of other relay sites across Dorset and Wiltshire, however these other relays do not carry the full range of Freeview channels. Freesat may be the only viable option to get additional free television channels in these areas. Relay sites (excluding Salisbury) did not carry digital TV until switchover.
The far west of Dorset (not coastal areas) may receive programmes from Stockland Hill transmitter in Devon, just past Axminster. This transmitter carries BBC South West and ITV Westcountry regional programmes. Some of Stockland Hill's commercial services co-channel with Rowridge. To counteract this, some of Stockland Hill's signals were boosted on 18th April. They may knock out reception of certain channels at Rowridge in parts of Dorset. However Stockland Hill's signals are all horizontally polarised so that some affected viewers who wish to stay with Rowridge and BBC South/ITV Meridian programmes can switch to vertical polarisation by adjusting their aerial. Local topography will dictate if this is possible or not. It may be possible to combine services from more than one transmitter by having two aerials. A reputable local aerial installer, familiar with the local area and quirks of reception in a given area will have the best knowledge.
- North East Hampshire
The North East of Hampshire is at the northern extremity of the Rowridge coverage area. Due to co-channel issues with Crystal Palace, the horizontally polarised signals of the commercial broadcasters are at a lower power. Use of an amplifier may boost interfering signals from Crystal Palace. The vertically polarised signals may be stronger. This will involve the change of the aerial axis as described above, and possibly in a location on the building shielded from the direction of London. Alternatively, viewers may wish to switch to using the Hannington transmitter where available, as this covers most places along the edge of Rowridge and Crystal Palace transmitter coverage zones. Likewise, some viewers receiving Crystal Palace some distance away from London in the north east of Hampshire may find a more reliable signal from another transmitter. Viewers may have historically opted for Crystal Palace reception because they commute to London, although another local service was available.
Whilst Hannington is almost always the best transmitter to aim for, the following examples show the variable reception of Rowridge and Crystal Palace TV signals in the North East of Hampshire and the affects of the co-channel interference between the two:
Using the example postcode RG22 4TT (SW edge of Basingstoke) on the Digital UK trade postcode checker, it can be seen that at this location, reception is possible from Hannington, Rowridge, Crystal Palace and Oxford transmitters. At this location, Crystal Palace is slightly stronger than Rowridge, but Rowridge's signals on the same frequencies as Crystal Palace knock out reception somewhat.
Use this link to see the chart, which shows that some of Crystal Palace's multiplexes are "red" - poor reception.
The ideal solution is not to use Crystal Palace or Rowridge, but to use Hannington. Due to the number of transmitters available in the Basingstoke area, some receivers may store the wrong services first, i.e. store channels from a more distant, weaker transmitter first. A manual retune to the UHF channels used by the strongest transmitter at a given location may be the only solution.
Just a short distance further down the M3, in the RG25 2BB postcode area, the tables are turned on Crystal Palace and Rowridge http://www.digitaluk.co.uk/postcodechecker/main/trade/RG25+2BB/NA/0/NA, but both still cancel each other out on UHF channels 22, 25 and 28 - hence no readings on three services.
Whereas in Four Marks - another relatively short hop away - example postcode GU34 5AZ - the postcode checker shows dominance for Rowridge, and a stronger signal for the vertically polarised service to cancel out Crystal Palace. Even though, Hannington remains the best to use. Interestingly, a service from Mendip in Somerset is predicted! http://www.digitaluk.co.uk/postcodechecker/main/trade/GU34+5AZ/NA/0/NA
A local aerial installer will be able to give the best advice on receiving digital services in a post-switchover environment and advice beyond the limitations of a 'one size fits all' internet article. Viewers receiving a from a transmitter other than the one predicted as 'most likely' in the database are more likely to be affected by recent changes.
Supporting information:UHF broadcast channels at Rowridge for manual tuning purposes